1. Field of the Invention
The present invention relates to a semiconductor device for use in electronic equipment, and a method for manufacturing the same, and more particularly to a semiconductor device which is improved in repair performance in a process for mounting a semiconductor chip on a circuit board based on a face-down system.
2. Description of the Related Art
In a face-down type semiconductor device as described above, as shown in FIG. 1, a projecting conductive bump 3 is formed at an external connection pad of a semiconductor chip 1, and a predetermined amount of liquefied thermosetting resin or liquefied photocurable or photosetting resin is coated at the center of a mount portion of the semiconductor chip of a circuit board 2. Thereafter, the conductive bump of the semiconductor chip 1 and an external connection pad 6 of the circuit board 2 are positioned to be positionally matched with each other. In the case of the thermosetting resin, the semiconductor chip is heated while the circuit board 3 is pressed to the semiconductor chip, and the thermosetting resin 5 is hardened, thereby coupling or joining the semiconductor chip 1 and the circuit board 2.
Further, in the case of the photocurable resin, after the semiconductor chip 1 and the circuit board 2 are positioned, the semiconductor chip 1 is pressed against the circuit board 2, and ultraviolet ray is irradiated to harden the photocurable resin, thereby coupling the semiconductor chip 1 and the circuit board 2.
Still further, Japanese Patent Application Laid-open No. Hei-5-6919 discloses a method (flip chip bonding method) for constructing this type of semiconductor device by using two types of resin. According to this method, a semiconductor chip is covered from the upper surface side of the semiconductor chip by an elastic member which is larger in size than the semiconductor chip, and the elastic member is fixed to a circuit board by thermoplastic resin to temporarily mount the semiconductor chip on the circuit board while the semiconductor chip is pressed and fixed onto the circuit board. Thereafter, photocurable resin is filled into the elastic member and sealed.
In a method of manufacturing a semiconductor device as shown in Japanese Patent Application Laid-open No. Hei-6-21117, a small amount of liquefied resin is transferred and supplied to the center of the chip by using a transfer method to temporarily fix the semiconductor chip to the circuit board by the resin, and then the same kind of liquefied resin is supplied to harden the resin and perfectly seal the semiconductor chip and the circuit board with the resin. In the case of this technique, the resin is filled into the gap between the circuit board or wiring board and the semiconductor chip and hardened.
In the semiconductor device as described above, the semiconductor chip and the circuit board are coupled to each other by using the hardening action of the sealing resin. In addition to the above type of semiconductor device, there is known another type of semiconductor device in which a conductive bump formed on a semiconductor chip and a connection pad of a circuit board are coupled to each other by solder, and then liquefied sealing resin is filled into the gap between the semiconductor chip and the circuit board and hardened. Such a type of semiconductor device is shown in FIG. 2 in which the conductive bump 3 of the semiconductor chip and the external connection pad 6 of the circuit board are connected to each other through solder 4.
A first problem of the above conventional technique is as follows. Since this type of semiconductor device uses thermosetting resin, repair cannot be performed when a semiconductor chip is recognized as a defective after the semiconductor chip and the circuit board are coupled to each other by hardening the resin.
In this type of semiconductor device, the semiconductor chip and the circuit board are adhesively attached to each other by hardening thermosetting resin or ultraviolet-ray curable resin, and electrically connected to each other as shown in FIGS. 1 and 2. Accordingly, even when the semiconductor chip is subsequently checked and judged as a defective, it is difficult to peel off the semiconductor chip together with the hardened thermosetting resin or the ultraviolet-ray curable resin without damaging the circuit board.
A second problem is as follows. According to the method disclosed in Japanese Patent Application Laid-open No. Hei-5-6919, the repair work can be performed after the semiconductor chip and the circuit board are temporarily fixed to each other. However, since the elastic member must be used in the semiconductor device so as to cover the semiconductor chip, it is impossible to design this type of semiconductor device in compact size and light weight, and high-density mounting is also impossible.
This is because the elastic member which is used for the temporary fixing is larger than the semiconductor chip and thus other parts cannot be mounted at the portion covered by the elastic member. Further, since the elastic member covers the semiconductor chip, the thickness of the elastic member increases the thickness of the semiconductor device.
A third problem is as follows. In the case of the method disclosed in Japanese Patent Application Laid-open No. Hei-6-21117, the resin is filled into the gap between the semiconductor chip and the circuit board and then hardened. This publication describes that a small amount of resin is first used to temporarily fix the semiconductor chip and the circuit board to each other and thus the semiconductor chip can be easily removed when the semiconductor chip is judged as a defective. However, this method uses curable (thermosetting or ultraviolet-ray curable) resin, and thus the repair work cannot be well performed.
The reason is as follows. Since the curable resin is used for the temporary fixing, the material of the curable resin is proximate to the material of the circuit board, and thus adhesion of the curable resin to the circuit board is good even when the amount of the resin is small. Therefore, when the semiconductor chip is removed from the circuit board, it is necessary to scrape the resin from the circuit board, so that the circuit board may be damaged.
A fourth problem is as follows. In this type of semiconductor device, the gap between the semiconductor chip and the circuit board is sealed by the resin. Particularly when the thermosetting resin is used, voids are formed in the sealing resin, and reliability of the semiconductor device is lowered.
The reason is as follows. Since the semiconductor chip is heated to a high temperature and the resin on the circuit board is rapidly heated and hardened by the heat of the semiconductor chip, residual solvent and monomers of low molecular weight in the resin are vaporized and remain in the hardened resin.
Further, in the case where the ultraviolet-ray curable resin is used, the process of heating the semiconductor chip to harden the resin is not needed. However, the ultraviolet ray is irradiated from the side surface to harden the resin while the semiconductor chip is pressed against the circuit board, and thus the ultraviolet ray is not sufficiently incident to the gap between the semiconductor chip and the circuit board because the gap is equal to several tens micrometers, so that hardening becomes insufficient. Accordingly, only a transparent glass substrate is usable as the circuit board. Therefore, this method is limited to a specific application, and it is unsuitable to general purposes.
A fifth problem is as follows. The external connection bump of the semiconductor chip which is electrically connected to the circuit board and the external connection pad of the circuit board are electrically connected while merely brought into contact with each other. Therefore, when a temperature cycle test is performed, it may be difficult to maintain the electrical connection between the semiconductor chip and the circuit board at a high temperature.
A sixth problem is as follows. The conductive bump of the semiconductor chip and the connection pad of the circuit board are connected to each other by only the solder. Therefore, when the sealing resin is filled into the gap between the semiconductor chip and the circuit board, cracks may occur in the solder during the resin sealing process and the resin hardening process. As described above, the conductive bump of the semiconductor chip and the connection pad of the circuit board are coupled by only the solder. In this case, the semiconductor chip is heated to about 250.degree. C. to melt the solder formed on the connection pad of the circuit board, thereby coupling the semiconductor chip and the circuit board. In this case, however, in the cooling progress of the chip, cracks occur in the coupling portion of the solder by stresses due to the difference in thermal expansion coefficient between the circuit board and the semiconductor chip and by impacts due to handling during the period from the mount step to the resin sealing step.